As for conventional methods for providing stiffness which is applied to a joint for a robot manipulator, there are a method using mechanical springs and a method which detects a force applied to a manipulator without any additional mechanism so as to control driving motors of a joint such that a virtual spring effect is exhibited.
The bulletin of “The Second Joint Workshop on Dependent Robots in Human Environments” [Korea Advanced Institute of Science and Technology, 2002, pp. 88-95] discloses a safe arm structure for robots to which mechanical springs are added. However, the structure cannot control stiffness depending on operations, and is operated with only a predetermined spring constant.
The bulletin of “The International Conference on Intelligent Robots and Systems” (1995, pp. 412-508) discloses a robot arm provided with a mechanical impedance controller. The robot arm disclosed in the literature is constructed so as to control stiffness by using a separate driving device. However, due to the use of the additional driving device, the robot arm cannot rapidly change stiffness.
The bulletin of “The International Conference on Robot and Automation” (2005, pp. 526-531) discloses a variable stiffness driver. The variable stiffness driver disclosed in the literature controls stiffness by using an additional mechanism such as a belt. Therefore, the volume of the variable stiffness driver increases. Further, the belt is associated with the problem of limited endurance.
The bulletin of “The International Conference on Robot and Automation” (2002, pp. 1710-1716) discloses a controller which includes a sensor capable of measuring the force and torque of a joint portion such that a virtual spring effect is exhibited in accordance with the information on the force and torque. However, the controller disclosed in the literature is without a countermeasure against electric breakdown. Further, since controlling is performed by only one controller, efficiency and performance are degraded.